JobManager can crash if its initialized after the app finished launching

[zkline101]

When the JobManager is constructed it registers the launch handler here. And the doc for that method says:

and I ran into a case where the JobManager was created too late and the app crashes. If you create the JobManager at the app level (in the ...App.swift file) that will make sure it gets created in time. This should either be in some doc or the tutorial or both.